Durability and Biological Response of a New Posterior Dynamic Stabilization System Using Polyethylene with Vitamin E

Objective. The purpose of this study was to evaluate the durability and biological response of a new Posterior Dynamic Stabilization system using polyethylene with vitamin E on the sliding surface. Summary of Background Data. The use of polyethylene with vitamin E on the sliding surface in Posterior Dynamic Stabilization has not been reported previously. Methods. A developed pedicle screw-based Posterior Dynamic system consists of four parts: a set screw, a rod, a ball, and a pedicle screw. The rod is inserted into the through hole of the ball, and the ball is sandwiched by the set screw. (1) Fatigue Wear Test. Testing was conducted under a dynamic compressive load of 50N at a speed of 1 Hz for 1 million cycles. We examined the loss of polyethylene due to abrasion in 3 units. (2) Biological Response in Pigs. In two pigs, a new pedicle screw and a conventional pedicle screw were inserted in L2 and L3/4, and L4 and L2/3, respectively. After breeding for 6 months, autopsies were performed. CT imaging was used to evaluate bone union of the facet joint. Abrasive specimens were prepared, and abrasion powder and inflammatory cell infiltration were evaluated microscopically. Results. The average loss of polyethylene due to abrasion was -0.01 mg. In all units, polyethylene showed a decrease of 0.1 mm or less at the contact point with the set screw. The facet joints between the conventional screws exhibited bone fusion, but the facet joint between the conventional and the new screw retained mobility with no bony fusion. No abrasion powder was found and inflammatory cell infiltration was only minimally observed. Conclusion. The new Posterior Dynamic Stabilization system exhibited a high level of durability and biological safety.

Dynamic stabilization for degenerative diseases in the lumbar spine: 2 years results

Following lumbar fusion, adjacent segment degeneration has been frequently reported. Dynamic systems are believed to reduce main fusion drawbacks. We conducted a retrospective study on patients with degenerative lumbar disease treated with posterior dynamic stabilization with monoaxial hinged pedicular screws and lumbar decompression. VAS and ODI were used to compare clinical outcomes. As radiological outcomes, LL and SVA were used. 51 patients were included with an average follow-up of 24 months. 13 patients were revised because of postoperative radiculopathy (n=4), subcutaneous hematoma(n=2), L5 screw malposition (n=1) and adjacent segment disease (n=6). The mean ODI score 41 preoperatively compared to 36 postoperatively. The mean VAS scores for back and leg pain were 5.3 and 4.2, respectively compared to 4.5 and 4.0 post-operatively. The mean SVA was 5.3 cm pre-operatively, and 5.7 cm postoperatively. The mean LL was 47.5° preoperatively and 45.5° postoperatively. From our data, whichfail to show significant improvements andreflect a high revision rate, we cannot generally recommend dynamic stabilization as an alternative to fusion. Comparative trials with longer follow-ups are required.